The aims of this study were 1) to determine which of three nebulizer systems could aerosolize sufficient tobramycin sulfate to achieve a peak sputum tobramycin concentration measured 10 minutes after the completion of nebulization in 85% of patients with CF and 2) determine whether the tobramycin concentration required to achieve a peak sputum tobramycin concentration is safe and well tolerated by the patients. This study has been completed and data is in analysis.